Azobenzene Photoswitching with Near-Infrared Light Mediated by Molecular Oxygen.

Efficient photoisomerization between the cis and the trans states of azobenzenes using low-energy light is desirable for a range of applications in, e.g., photobiology yet challenging to accomplish directly with modified azobenzenes. Herein, we utilize molecular iodine as a photocatalyst to induce indirect cis-to-trans isomerization of 4,4'-dimethoxyazobenzene with 770 nm near-infrared light, showing robustness during more than 1000 cycles in ambient conditions. Intriguingly, the catalysis is mediated by molecular oxygen, and we demonstrate that other singlet-oxygen-generating photosensitizers besides iodine, i.e., palladium phthalocyanine, catalyze the isomerization as well. Thus, we envision that the approach can be further improved by employing other catalysts with suitable photoelectrochemical properties. Further studies are needed to explore the applicability of the approach with other azobenzene derivatives.

Halogen bonding stabilizes a cis-azobenzene derivative in the solid state: a crystallographic study.

Crystals of trans- and cis-isomers of a fluorinated azobenzene derivative have been prepared and characterized by single-crystal X-ray diffraction. The presence of F atoms on the aromatic core of the azobenzene increases the lifetime of the metastable cis-isomer, allowing single crystals of the cis-azobenzene to be grown. Structural analysis on the cis-azobenzene, complemented with density functional theory calculations, highlights the active role of the halogen-bond contact (N...I synthon) in promoting the stabilization of the cis-isomer. The presence of a long aliphatic chain on the azobenzene unit induces a phase segregation that stabilizes the molecular arrangement for both the trans- and cis-isomers. Due to the rarity of cis-azobenzene crystal structures in the literature, our paper makes a step towards understanding the role of non-covalent interactions in driving the packing of metastable azobenzene isomers. This is expected to be important in the future rational design of solid-state, photoresponsive materials based on halogen bonding.

Benchmarking DFT methods with small basis sets for the calculation of halogen-bond strengths.

In recent years, halogen bonding has become an important design tool in crystal engineering, supramolecular chemistry and biosciences. The fundamentals of halogen bonding have been studied extensively with high-accuracy computational methods. Due to its non-covalency, the use of triple-zeta (or larger) basis sets is often recommended when studying halogen bonding. However, in the large systems often encountered in supramolecular chemistry and biosciences, large basis sets can make the calculations far too slow. Therefore, small basis sets, which would combine high computational speed and high accuracy, are in great demand. This study focuses on comparing how well density functional theory (DFT) methods employing small, double-zeta basis sets can estimate halogen-bond strengths. Several methods with triple-zeta basis sets are included for comparison. Altogether, 46 DFT methods were tested using two data sets of 18 and 33 halogen-bonded complexes for which the complexation energies have been previously calculated with the high-accuracy CCSD(T)/CBS method. The DGDZVP basis set performed far better than other double-zeta basis sets, and it even outperformed the triple-zeta basis sets. Due to its small size, it is well-suited to studying halogen bonding in large systems.

Efficient Light-Induced Phase Transitions in Halogen-Bonded Liquid Crystals.

Here, we present a new family of light-responsive, fluorinated supramolecular liquid crystals (LCs) showing efficient and reversible light-induced LC-to-isotropic phase transitions. Our materials design is based on fluorinated azobenzenes, where the fluorination serves to strengthen the noncovalent interaction with bond-accepting stilbazole molecules, and increase the lifetime of the cis-form of the azobenzene units. The halogen-bonded LCs were characterized by means of X-ray diffraction, hot-stage polarized optical microscopy, and differential scanning calorimetry. Simultaneous analysis of light-induced changes in birefringence, absorption, and optical scattering allowed us to estimate that <4% of the mesogenic units in the cis-form suffices to trigger the full LC-to-isotropic phase transition. We also report a light-induced and reversible crystal-to-isotropic phase transition, which has not been previously observed in supramolecular complexes. In addition to fundamental understanding of light-responsive supramolecular complexes, we foresee this study to be important in the development of bistable photonic devices and supramolecular actuators.

A Developability-Focused Optimization Approach Allows Identification of in Vivo Fast-Acting Antimalarials: N-[3-[(Benzimidazol-2-yl)amino]propyl]amides.

Malaria continues to be a major global health problem, being particularly devastating in the African population under the age of five. Artemisinin-based combination therapies (ACTs) are the first-line treatment recommended by the WHO to treat Plasmodium falciparum malaria, but clinical resistance against them has already been reported. As a consequence, novel chemotypes are urgently needed. Herein we report a novel, in vivo active, fast-acting antimalarial chemotype based on a benzimidazole core. This discovery is the result of a medicinal chemistry plan focused on improving the developability profile of an antichlamydial chemical class previously reported by our group.

Synthesis and biological evaluation of 2-arylbenzimidazoles targeting Leishmania donovani.

A set of 56 2-arylbenzimidazoles was designed, synthesized and tested against Leishmania donovani amastigotes. The left- and right-hand side rings of the molecule, as well as the amide linker were modified. Structurally different derivatives were screened on L. donovani axenic amastigotes at concentrations of 5, 15 and 50 µM, and the ten most active derivatives were selected for further testing. 2-Arylbenzimidazole derivative 24 was active against L. donovani-infected THP-1 cells showing 46% parasite inhibition at 5 µM.

Conformation study of 2-arylbenzimidazoles as inhibitors of Chlamydia pneumoniae growth.

Chlamydia pneumoniae is a worldwide cause of various respiratory track diseases ranging from asymptomatic pharyngeal infection to severe, sometimes fatal pneumonia. We have previously identified 2-arylbenzimidazoles as highly active antichlamydial compounds. In this work the importance of conformational effects on the structure-activity relationship of these compounds was studied. To simplify calculations, properly substituted N-phenylbenzamides, or the corresponding heterocyclic compounds, and 2-arylbenzimidazoles were used as model compounds. They were energy minimized and the energy differences between certain conformations were calculated. The main finding was that the compounds which can more easily adopt a non-planar conformation show higher bioactivity. This finding can be utilized in designing new derivatives or in constructing a pharmacophore model.

Design and synthesis of 2-arylbenzimidazoles and evaluation of their inhibitory effect against Chlamydia pneumoniae.

Chlamydia pneumoniae is an intracellular bacterium that responds poorly to antibiotic treatment. Insufficient antibiotic usage leads to chronic infection, which is linked to disease processes of asthma, atherosclerosis, and Alzheimer's disease. The Chlamydia research lacks genetic tools exploited by other antimicrobial research, and thus other approaches to drug discovery must be applied. A set of 2-arylbenzimidazoles was designed based on our earlier findings, and 33 derivatives were synthesized. Derivatives were assayed against C. pneumoniae strain CWL-029 in an acute infection model using TR-FIA method at a concentration of 10 µM, and the effects of the derivatives on the host cell viability were evaluated at the same concentration. Fourteen compounds showed at least 80% inhibition, with only minor changes in host cell viability. Nine most potential compounds were evaluated using immunofluorescence microscopy on two different strains of C. pneumoniae CWL-029 and CV-6. The N-[3-(1H-benzimidazol-2-yl)phenyl]-3-methylbenzamide (42) had minimal inhibitory concentration (MIC) of 10 µM against CWL-029 and 6.3 µM against the clinical strain CV-6. This study shows the high antichlamydial potential of 2-arylbenzimidazoles, which also seem to have good characteristics for lead compounds.

Inhibitory effect of the natural product betulin and its derivatives against the intracellular bacterium Chlamydia pneumoniae.

Chlamydia pneumoniae is a universal pathogen that has been indicated to play a part in the development of asthma, atherosclerosis and lung cancer. The complete eradication of this intracellular bacterium is in practice impossible with the antibiotics that are currently in use and studies on new antichlamydial compounds is challenging because Chlamydia research lacks the tools required for the genetic modification of this bacterium. Betulin is a natural lupane-class triterpene derived from plants with a wide variety of biological activities. This compound group thus has wide medical potentials, and in fact has been shown to be active against intracellular pathogens. For this reason, betulin and its derivatives were selected to be assayed against C. pneumoniae in the present study. Thirty-two betulin derivatives were assayed against C. pneumoniae using an acute infection model in vitro. Five promising compounds with potential lead compound characteristics were identified. Compound 24 (betulin dioxime) gave a minimal inhibitory concentration (MIC) of 1 microM against strain CWL-029 and showed activity in nanomolar concentrations, as 50% inhibition was achieved at 290 nM. The antichlamydial effect of 24 was confirmed with a clinical isolate CV-6, showing a MIC of 2.2 microM. Previous research on betulin and its derivatives has not identified such a remarkable inhibition of Gram-negative bacterial growth. Furthermore, we also demonstrated that this antichlamydial activity was not due to PLA(2) (EC 3.1.1.4) inhibition caused by the betulin derivatives.

Pharmacological characterization of noroxymorphone as a new opioid for spinal analgesia.

BACKGROUND: Noroxymorphone is one of the major metabolites of oxycodone. Although oxycodone is commonly used in the treatment of acute and chronic pain, little is known about the antinociceptive effects of noroxymorphone. We present an in vivo pharmacological characterization of noroxymorphone in rats. METHODS: The antinociceptive properties of noroxymorphone were studied with thermal and mechanical models of nociception in rats. RESULTS: Intrathecal noroxymorphone (1 and 5 microg/10 microL) induced a significantly longer lasting antinociceptive effect compared with oxycodone (200 microg/10 microL) and morphine (1 and 5 microg/10 microL). Pretreatment with subcutaneous naloxone (1 mg/kg) 15 min before intrathecal drug administration significantly decreased the antinociceptive effect of both noroxymorphone and morphine, indicating an opioid receptor-mediated antinociceptive effect. In the hotplate, paw pressure, and tail flick tests, subcutaneous noroxymorphone was inactive in doses of 5, 10, and 25 mg/kg. Also, no effect on motor function was observed in the rotarod test with doses studied. No antihyperalgesic effect was observed in the carrageenan model for inflammation in rats with subcutaneous noroxymorphone 25 mg/kg. CONCLUSIONS: The results of this study indicate that noroxymorphone is a potent mu-opioid receptor agonist when administered intrathecally. The lack of systemic efficacy may indicate reduced ability of noroxymorphone to penetrate the blood-brain barrier due to its low calculated logD value (log octanol/water partition coefficient). Thus, noroxymorphone should have a negligible role in analgesia after systemic administration of oxycodone. Because of its spinal efficacy and long duration of effect, noroxymorphone is an interesting opioid for spinal analgesia with a low potential for abuse. Its safety for spinal administration should be assessed before clinical use.

Eudismic analysis of tricyclic sesquiterpenoid alcohols: lead structures for the design of potent inhibitors of the human UDP-glucuronosyltransferase 2B7.

The epimeric tricyclic sesquiterpenoid alcohols globulol, epiglobulol, cedrol, epicedrol, longifolol, and isolongifolol were investigated in their ability to inhibit the recombinant human UDP-glucuronosyltransferase (UGT) 2B7. The stereoisomers displayed rapidly reversible competitive inhibition, which was substrate-independent. Longifolol and its stereoisomer isolongifolol displayed the lowest competitive inhibition constants (K(ic)) of 23 and 26 nM, respectively. The K(ic) values of cedrol and its epimer epicedrol were 0.15 and 0.21 microM, those of globulol and epiglobulol were 5.4 and 4.0 microM, respectively. The diastereomeric alcohols exhibited nearly identical affinities toward UGT2B7 indicating that the spatial arrangement of the hydroxy group had no influence on the dissociation of the enzyme-terpenoid complex. The high affinities stemmed presumably from mere hydrophobic interactions between the hydrocarbon scaffold of the terpenoid alcohol and the binding site of the enzyme. Glucuronidation assays revealed that there were large differences in the rates at which the epimeric alcohols were conjugated. Therefore, the spatial arrangement of the hydroxy group controlled the rate of the UGT2B7-catalyzed reaction. The introduction of a methyl group into the side chain of isolongifolol and longifolol increased the steric hindrance. As a result, the rate of the UGT2B7-catalyzed reaction was decreased by more than 88%. The findings indicated that the rate of the UGT2B7-catalyzed glucuronidation is significantly controlled by stereochemical and steric factors. Considering the high inhibition levels exerted by the tricyclic sesquiterpenoid alcohols, these compounds might serve as valuable lead structures for the design of potent inhibitors for UGT2B7.

Isoform-selective inhibition of the human UDP-glucuronosyltransferase 2B7 by isolongifolol derivatives.

A set of 48 derivatives of the tricyclic sesquiterpenol alcohol isolongifolol was synthesized. The set comprised homochiral and diastereomeric alcohols, amines, chlorohydrins, as well as carboxylic acids, phosphonic acids, and their corresponding esters. The absolute configuration of the epimeric compounds was assigned by 2D NMR experiments [gradient heteronuclear single quantum correlation (gHSQC) and gradient nuclear Overhauser enhancement spectroscopy (gNOESY)] in agreement with crystallographic data. The tricyclic derivatives were assessed as inhibitors of the human UDP-glucuronosyltransferase (UGT) 2B7. The phenyl-substituted secondary alcohol 26b was the best inhibitor in this series and its competitive inhibition constant was 18 nM. Compound 26b was not glucuronidated by UGT2B7 and other hepatic UGT enzymes, presumably due to the high steric hindrance exerted by its bulky phenyl substituent. Its inhibitory activity toward 14 other UGT isoforms of subfamily 1A and 2B was determined, and the data indicated that the tricyclic secondary alcohol 26b was highly selective for UGT2B7 (true selectivity >1000).

Potent inhibitors of the human UDP-glucuronosyltransferase 2B7 derived from the sesquiterpenoid alcohol longifolol.

The tricyclic sesquiterpenol (+)-longifolol served as a lead structure for the design of inhibitors of the human UDP-glucuronosyltransferase (UGT) 2B7. Twenty-four homochiral and epimeric longifolol derivatives were synthesized and screened for their ability to inhibit the enzyme. The absolute configuration at the stereogenic center C1' was determined by X-ray crystallography and 2D NMR spectroscopy (gHSQC, gNOESY). The phenyl-substituted secondary alcohol 16 b (beta-phenyllongifolol) displayed the highest affinity toward UGT2B7, and its inhibitory dissociation constant was 0.91 nM. The mode of inhibition was rapidly reversible and competitive. The inhibitor was not glucuronidated by UGT2B7 or other hepatic UGTs, presumably as a result of the high steric demand exerted by the phenyl group. Inhibition assays employing 14 other UGT isoforms suggested that inhibitor 16 b was highly selective for UGT2B7.

Antinociception by spinal and systemic oxycodone: why does the route make a difference? In vitro and in vivo studies in rats.

BACKGROUND: The pharmacology of oxycodone is poorly understood despite its growing clinical use. The discrepancy between its good clinical effectiveness after systemic administration and the loss of potency after spinal administration led the authors to study the pharmacodynamic effects of oxycodone and its metabolites using in vivo and in vitro models in rats. METHODS: Male Sprague-Dawley rats were used in hot-plate, tail-flick, and paw-pressure tests to study the antinociceptive properties of morphine, oxycodone, and its metabolites oxymorphone and noroxycodone. Mu-opioid receptor agonist-stimulated GTPgamma[S] autoradiography was used to study G-protein activation induced by morphine, oxycodone, and oxymorphone in the rat brain and spinal cord. Spontaneous locomotor activity was measured to assess possible sedation or motor dysfunction. Naloxone and the selective kappa-opioid receptor antagonist nor-binaltorphimine were used to study the opioid receptor selectivity of the drugs. RESULTS: Oxycodone showed lower efficacy and potency to stimulate GTPgamma[S] binding in the spinal cord and periaqueductal gray compared with morphine and oxymorphone. This could relate to the fact that oxycodone produced only weak naloxone-reversible antinociception after intrathecal administration. It also suggests that the metabolites may have a role in oxycodone-induced analgesia in rats. Intrathecal oxymorphone produced strong long-lasting antinociception, whereas noroxycodone produced antinociception with very high doses only. Subcutaneous administration of oxycodone and oxymorphone produced thermal and mechanical antinociception that was reversed by naloxone but not by nor-binaltorphimine. Oxymorphone was more potent than oxycodone, particularly in the hot-plate and paw-pressure tests. CONCLUSIONS: The low intrathecal potency of oxycodone in rats seems be related to its low efficacy and potency to stimulate mu-opioid receptor activation in the spinal cord.

Chiral distinction between the enantiomers of bicyclic alcohols by UDP-glucuronosyltransferases 2B7 and 2B17.

The stereoselective binding and transformation of optically pure bicyclic alcohols by human UDP-glucuronosyltransferases from subfamily 2B were investigated. The enantiomers of 1-indanol, 1-tetralol, and 1-benzosuberol were synthesized by asymmetric Corey-Bakshi-Shibata reduction and subjected to glucuronidation assays. The alcohols studied were primarily glucuronidated by UGT2B7 and UGT2B17. The catalytic transformation by UGT2B17 was highly stereoselective, favoring conjugation of the (R)-enantiomers. UGT2B7, on the other hand, did not exhibit stereoselectivity toward 1-benzosuberol, the best substrate in this series. To assess binding affinities to the enzymes, the six different compounds were tested for their efficiency as inhibitors of either UGT2B7 or UGT2B17. The results of the latter analyses indicated that the affinities of both enantiomers of each pair towards UGT2B7 and UGT2B17 were of the same order of magnitude. Therefore, the findings of this study suggest that the spatial arrangement of the hydroxy group plays an important role in the glucuronic acid transfer reaction, but not necessarily in substrate binding to the UGTs.

Similarity based virtual screening: a tool for targeted library design.

High throughput screening drug discovery utilizes large and expensive compound libraries. As an alternative, a smaller targeted library can be constructed with the aid of the 3D structure of the target molecule. We used the X-ray crystal structure of a protein homologous to the selected target in creation of a small focused library and evaluated inhibition potential of this library against Chlamydia pneumoniae, a common pathogen recently linked to atherosclerosis and risk of myocardial infarction.

Stereochemical sensitivity of the human UDP-glucuronosyltransferases 2B7 and 2B17.

A set of 28 enantiomers comprising rigid and flexible secondary alcohols was synthesized by the asymmetric Corey-Bakshi-Shibata reduction. The enantiomerically pure alcohols were subjected to enzymatic glucuronidation assays employing the human UDP-glucuronosyltransferases (UGTs) 2B7 and 2B17. Both UGTs displayed high levels of stereoselectivity, favoring the conjugation of the (R)-enantiomers over their respective (S)-stereoisomers at eudismic ratios up to 256. The spatial arrangement of the hydroxy group determined the diastereoselectivity of the UGT2B17-catalyzed reaction in agreement with Pfeiffer's rule (eudismic activity quotient = 0.83 +/- 0.14). Inhibition studies revealed that the enantiomers had similar affinities toward the enzymes. The diastereoselectivity of the UGT-catalyzed conjugation stemmed, therefore, from the arrangement of the substrates in the catalytic site, rather than from distinct affinities toward the enzymes. Taken together, this study showed that metabolic enzymes that are generally conceived to be rather "flexible" in nature are capable of displaying high levels of chiral distinction.